Usually, a polymer composite with a viscoelastic response matrix has a creep behavior. To predict this phenomenon, a good knowledge of the properties and mechanical constants of the material becomes important. Schapery’s equation represents a basic relation to study the nonlinear viscoelastic creep behavior of composite reinforced with carbon fiber (matrix made by polyethrtethrtketone (PEEK) and epoxy resin). The finite element method (FEM) is a classic, well known and powerful tool to determine the overall engineering constants. The method is applied to a fiber one-directional composite for two different applications: carbon fibers T800 reinforcing an epoxy matrix Fibredux 6376C and carbon fibers of the type IM6 reinforcing a thermoplastic material APC2. More cases have been considered. The experimental results provide a validation of the proposed method and a good agreement between theoretical and experimental results.

The aim of this paper is to present some important practical cases in the analysis of the creep response of unidirectional fiber-reinforced composites. Some of the currently used models are described: the micromechanical model, homogenization technics, the Mori–Tanaka method, and the finite element method (FEM). Each method was analyzed to determine its advantages and disadvantages. Regarding the accuracy of the obtained results, comparisons are made with experimental tests. The methods presented here are applied to carbon-fiber-reinforced composites, but these considerations can also be applied to other types of composite materials.

The homogenization theory, used for the study of differential equations with periodic coefficients, with a rapid variation, is used in the paper for the analysis of the creep phenomenon of composite materials, reinforced with fibers. Generally, a polymer composite having a matrix with a viscoelastic response manifests a creep behavior. A good knowledge of mechanical constants allows us to predict the time response under the action of a load, which is important in engineering. The homogenization method is used to determine the engineering constants for a composite reinforced with carbon fibers. The method is applied for the particular case of fiber-reinforced unidirectional composites to obtain the equations that finally offer the required values. The epoxy matrix Fibredux 6376C is reinforced with carbon fibers T800 and the thermoplastic specimens made by APC2 material is reinforced with carbon fibers of the type IM6. The experimental results give a good concordance with the theoretical predictions.

In the paper, using the video image correlation method, a study of the micro-movement pattern of the dental implant and of a normal was performed. It is revealed that there are great differences between these two situations. The linear displacement type of the dental implant refers to the linear elastic modulus of bone tissue in the case of normal bite forces. It seems that the major influencing factor regarding the type and value of implant micro-movement is defined by the underlying bone tissue. It is to be considered that masticator force transmission inside a more stiff and dense bone could be attenuated by the antagonist teeth parodontium, dental implant and abutment connection type, and the elastic modulus of material of the dental crown. Because of the elasticity of the periodontal ligament system, during the loading of the dental implant, the natural tooth has been displaced slightly more, leaving the dental implant in an unfavorable position, having to bear the full amount of loading forces. When comparing the relative displacements in the case of the loaded tooth, it is shown that the dental implant has been moving almost symmetrically with the tooth. This could mean that large amounts of forces are transmitted towards the periimplant bone tissue, but in a more optimal, parabolic manner due to the action of the periodontal ligaments surrounding the natural tooth.

Heat transfer analysis can be studied efficiently with the help of so-called modern dimensional analysis (MDA), which offers a uniform and easy approach, without requiring in-depth knowledge of the phenomenon by only taking into account variables that may have some influence. After a brief presentation of the advantages of this method (MDA), the authors applied it to the study of heat transfer in straight bars of solid circular section, protected but not thermally protected with layers of intumescent paints. Two cases (two sets of independent variables) were considered, which could be easily tracked by experimental measurements. The main advantages of the model law obtained are presented, being characterized by flexibility, accuracy, and simplicity. Additionally, this law and the MDA approach allow us to obtain much more advantageous models from an experimental point of view, with the geometric analogy of the model with the prototype not being a necessary condition. To the best knowledge of the present authors there are no studies reporting the application of the MDA method as it was used in this paper to heat transfer.